From: Krivo, Stan

Sent: Thursday, March 14, 2013 10:09 AM

To: Bart Brashers

Cc: Shepherd, Lorinda
Subject: Statoil Updated Air Quality Analysis

- Remaining Issues

Bart,

I have reviewed the second response to our review comments on Statoil’ s Title V/PSD Permit
Application for OCS drilling and exploration activities in the Eastern Gulf of Mexico (EGOM) and the updated air quality modeling analysis (UAQMA) contained as Attachment 1 to the response

letter. To complete this review, the followin g items from the UAQMA need further information/explanations.

Revised Section 6

- Air Quality Impact Assessment (January 2013)

Stack Exit Parameters

– The following comments are associated with the modeled stack exit parameters provide in Tables 6.2.3

- 1, 2, and 3.

- The units for the columns Exit Velocity and Exit Temperature are incorrect (meters) in Tables

6.2.3

- 1 and 2. The correct units should be provided.

- All stacks with horizontal stack orientation were indicated to be modeled with an exit vel ocity

of 0.001 m/s. Horizontal stacks in Table 6.2.3

- 3 are not adjusted to this value and appear to have been used in the impact modeling.

- The basis for the stack heights should be provided (e.g., water surface or vessel deck).

Volume Sources

– The fol lowing comments are associated with Tables 6.2.3

- 4 and 5.

- The forklifts are associated with the Discoverer America drill ship and their emissions have

been included with the Discoverer America in Attachment 2 emission calculations. The reason

the forkli fts are included with the support vessel as a volume source should be explained.

- The vertical dimension of the modeled representative volume sources was the average height of the offshore support vessels divided by 2.15 (29.5 m or 96.6 feet). The heigh ts of the fleet of available support vessels used to develop this height should be provided.

- The horizontal dimension for the representative volume sources are for both the longitudinal

and lateral dimensions. The horizontal dimension modeled was the c enter to center distance between adjacent volume sources divided by 2.15 (5,121 m for long

- term and 1,664 m for short

term). This appears not appropriate for the lateral path dimension and not following the guidance provided in the AERMOD User’s Guide for volume sources. Further explanation and/or demonstration of the appropriateness of the support vessels modeling procedure should be provided.

- The volume source heights were indicated to be based on SCREEN3 runs using actual stack parameters, building d imensions bases on ship’s dimensions, stability of 4, and wind speed of 20

m/s. As noted above for Table 6.2.3

- 3, the crew boat horizontal stacks should have been modeled with 0.001 m/s exit velocity. Review of the SCREEN3 modeling files reveals no

build ing dimensions were used for these supply boats and the selected plume height for the crew boats was associated with 3 stability and 8 m/s. The bases for the heights (19.41 m) of the volume sources should be provided and explained.Recent Court Decision

- PM2.5 SMC and SIL

- The recent court decision concerning use of the

PM2.5 significant monitoring concentration (SMC) and significant impact levels (SIL) as the basic for exemption from pre

- construction air quality monitoring and cumulative NAAQS and

PSD increment compliance modeling affects this application.

- The court has vacated and remained the PM2.5 SIL. Project impacts less than the SIL cannot, by itself, be used as justification to eliminate cumulative NAAQS and PSD increment compliance modeling. Additional information should be provided to support a conclusion that the project’s impacts would not cause or contribute to a NAAQS or PSD increment exceedance.

- The court also vacated the PM2.5 SMC. Project impacts less than the SMC can no longer b e used to exempt the project from pre

- construction ambient air quality monitoring. If existing air quality observations are proposed in lieu of pre

- construction monitoring, supporting information should be provided to demonstrate that existing ambient air quality data would provide representative or conservative ambient concentrations for the impact area.

PSD Class I Area Air Quality Related Values (AQRV) Assessment

- The federal land managers

for the Breton Class I area should be provided an opportunity to review and comment on the updated PSD Class I area AQRV impact analyses.

Please let me know if you have any questions. Thanks...sjk

Stanley J. Krivo
U.S. Environmental Protection Agency
Atlanta Federal Center, 61 Forsyth Street, SW
Atlanta, GA 30303 404/562

- 9123 (Phone) 404/562

- 9091 (Fax)